Evidence alone don't win cases
Majority of people think that presence of evidence can win a legal case. It is the job of the lawyer to get them admitted in the court which is not simple when the opposing lawyer is a seasoned lawyer.
Laws prohibit courts to consider evidence obtained through illegal means, unreliable hearsay statements, uncorroborated photocopies or duplicate audio video records, contaminated evidence, etc.
Some communications cannot be used as evidence in court without consent of parties to such communications as they are protected by law. For example spousal communications, doctor-patient confidential communications, advocate-client work products and communications, etc.
Even some people who held important position in Government are restricted to give statement in Court. If you have watched a recent biographical movie The Trial of the Chicago 7 in which Ramsey Clark testified in the Chicago Seven trial. He was barred by Judge Julius Hoffman from testifying before the jury after Clark had testified outside the presence of the jury. Judge Hoffman upheld the prosecution's objections to 14 of Defense Attorney William Kunstler's 38 questions to Clark, but Clark did testify that he had told the prosecutor Tom Foran to investigate the charges against the defendants through Justice Department lawyers "as is generally done in civil rights cases", rather than through a grand jury.
For Law enthusiasts I suggest some TV shows or movie that depicts near exact court procedures.
The Practice by David E Kelley
A Civil Action by Steven Zaillian
There is a quote given by a character in "A Civil Action" that I found to be interesting. I share it below:
:  The odds of a plaintiff's lawyer winning in civil court are two to one against. Think about that for a second. Your odds of surviving a game of Russian roulette are better than winning a case at trial. 12 times better. So why does anyone do it? They don't. They settle. Out of the 780,000, only 12,000 or 11/2 percent ever reach a verdict. The whole idea of lawsuits is to settle, to compel the other side to settle. And you do that by spending more money than you should, which forces them to spend more money than they should, and whoever comes to their senses first loses. Trials are a corruption of the entire process and only fools who have something to prove end up ensnared in them. Now when I say prove, I don't mean about the case, I mean about themselves.